1. Field of the Invention
The present invention relates to a liquid crystal display device.
2. Description of the Related Art
In a liquid crystal display device, including a pair of substrates which are opposing to each other with an interval, a plurality of pixel electrodes arranged in matrix, a plurality of thin film transistors provided in a corresponding manner to the plurality of pixel electrodes to be connected thereto, and a plurality of gate lines and signal lines for supplying a gate signal and date signal to each of corresponding thin film transistors are formed on one of the substrates. Moreover, common electrodes (opposite electrodes) which commonly oppose the plurality of pixel electrodes are formed on the other substrate. Then, liquid crystal is sealed in between the pair of substrates. Here, on each of the opposing surfaces of the pair of substrates, an alignment layer for regulating initial orientation state of liquid crystal molecules is provided. Then, in the liquid crystal display device orientation state of the liquid crystal changes when voltage is applied to a liquid crystal layer via the pixel electrodes of each pixel.
Especially in a vertical aligned liquid crystal display device disclosed in the JP 2008-83389A, protrusions are provided to one of the substrates so that liquid crystal molecules, which are oriented vertically to the substrate when voltage is not applied to the liquid crystal layer, can stably carry out orientation change when voltage is applied to the liquid crystal layer. In the vertical aligned liquid crystal display device having a substrate where protrusions are provided, liquid crystal molecules are oriented in a radial manner with each of the protrusions as its center when voltage is applied to the liquid crystal layer.
However, for example, because a thin film transistor is provided in the vicinity of the pixel electrode, an electric field generated by the gate electrode of the thin film transistor or the gate line connected to the gate electrode effects an electric field generated in a pixel electrode region. That is, if a spot having a different potential partially exists in the periphery of the pixel electrode, generation state of an electric field in this spot differs from other spots, and in such a case distortion is generated in the orientation state of liquid crystal molecules which are to be oriented in a radial fashion.
For example, as shown in FIG. 9, liquid crystal molecules 102 above a pixel electrode 101 connected to a thin film transistor 100 is influenced by an electric field of a gate electrode 100a and is pulled to a direction of an arrow in the figure. Then, center of liquid crystal orientation does not become a protrusion 103 but is shifted toward the gate electrode 100a. Thus, if distortion is generated in radial orientation of the molecules, there occurs a problem that visual scope differs by every direction and viewing angle performance is lowered.
Moreover, in a case where an external pressure is applied from a surface of the liquid crystal display device to temporarily change a cell gap and center position of the radial orientation is shifted from the protrusion along with the change, if there exists a spot where generation state of electric field differs in the periphery of the pixel electrode, the center positions of the radial orientation of some pixels do not return to the position of the protrusions but are trapped in the positions where generation state of electric field differs, for example, a position in the vicinity of the gate electrode of the thin film transistor. Thus, there occurs a problem that orientation state is transformed into a state which is different from the radial orientation. That is, even if the surface is pressed by a relatively weak force, there occurs a problem that variation in orientation state between pixels occurs and display quality is lowered.